OFFSET
1,2
COMMENTS
A deceptively correct-looking approximation to Pi/2.
LINKS
J. M. Borwein, P. B. Borwein and K. Dilcher, Pi, Euler numbers and asymptotic expansions, Amer. Math. Monthly, 96 (1989), 681-687.
J. M. Borwein, P. B. Borwein and K. Dilcher, Pi, Euler numbers and asymptotic expansions, Amer. Math. Monthly, 96 (1989), 681-687.
J. M. Borwein and R. M. Corless, Review of "An Encyclopedia of Integer Sequences" by N. J. A. Sloane and Simon Plouffe, SIAM Review, 38 (1996), 333-337.
EXAMPLE
Pi/2: 1.570796326794896619231321691639751442098584699687552910487472...
This sum: 1.570786326794897619231321191639752052098583314687557962587445...
..........================^=================^^^======^^^^=====^=^^^===^^...
MATHEMATICA
RealDigits[2*Sum[(-1)^(k-1)/(2k-1), {k, 50000}], 10, 130][[1]] (* Harvey P. Dale, Oct 23 2012 *)
CROSSREFS
KEYWORD
AUTHOR
EXTENSIONS
Entry revised by N. J. A. Sloane, Sep 08 2012
STATUS
approved